Non-Random Uncoiling in Heterobrachial Chromosomes.

second gamete. In each case, the broken end of the second chromosome 9 had no unsaturated end with which it could unite. As expected, this single broken end thereafter healed. Conclusions.-The experiments outlined allow some specific answers to be given to the questions presented in the first paragraph of this paper. Question (1) may be answered in the negative. Two chromosomes do not have to be in contact at the time of breakage in order that fusions may occur between their broken ends. This was shown by the fusion that occurred in the zygote or in an early embryonic nucleus between a broken end of chromosome 9 contributed by the male gamete and a broken end of the chromosome 9 contributed by the female gamete. Question (2) may be answered in the affirmative. This was shown by the fusion of these two chromosomes, which produced a dicentric chromosome, and the subsequent behavior of this dicentric chromosome which, for some time, followed the chromosomal type of breakage-fusion-bridge cycle. Question (3) cannot be answered directly from the present observations. Nevertheless, the observations imply that some force exists which accounts for the fusion of unsaturated broken ends of chromosomes. Question (4) likewise cannot be answered directly. Nevertheless, it is certain that the unsaturated state does not persist indefinitely. An unsaturated broken end will become saturated or healed and incapable of fusions when only one such broken end is present in sporophytic tissues;' or, as shown in this report, two such broken ends may heal without fusions even when these two ends are present in the same nucleus.